**6.3. POPs**

It is a generally accepted fact that that persistent organic pollutants (POPs) cause harm to human and animal tissue, earning them a reputation of 'the most widespread and toxic group of pollutants', as well as 'poisons without passports' [74-78]. Humans and animals worldwide were found to be carriers of POPs; from trace up to harmful amounts in their bodies [79-81]. Persistent organic pollutants include the chlorinated pesticides aldrin, dieldrin, dichlorodiphenyltrichloroethane (DDT), endrin, heptachlor, hexachlorobenzene, mirex and toxaphene, as well as industrial chemicals like PCBs, and the unwanted waste byproducts polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/F), and brominated flame retardants [75]. These chemicals have common, but distinct chemical and physical characteristics including:


 POPs have adverse effects in human and animal tissue even at very low concentrations. Some of these compounds disrupt normal biological functions, including hormone and other chemical messengers leading to metabolic conditions [79];

140 New Approaches to the Study of Marine Mammals

of these metals on marine mammals.

**6.3. POPs** 

characteristics including:

processes of break-down;

orientation and space perceptions in these sperm whales [73].

metals may be found in solution in the water column, as colloids, as suspended particles or absorbed to particulate matter [71]. The latter form often ends up as a constituent of the sediment and at least a portion is released again into the water column. It is also important to realize and take into account that not all sources of heavy metals are anthropogenic. The Mediterranean Sea for example is known for its natural high levels of Hg, and likewise the Arctic Sea for higher cadmium (Cd) concentrations [72]. Furthermore, different organs tend to accumulate different heavy metals, and are therefore metal specific. Heavy metals enter cetaceans through their lungs, skin (absorption), from the mother during gestation, through milk during nursing, as well as by ingestion of sea water and food. Also, mysticetes seem to be less affected by heavy metal accumulation as a result of their position in the food chain, when compared to odontocetes that occupy the top level. Interestingly, heavy metal levels are higher in older individuals and nonbreeding females. All these factors should be taken into account in studies on the effects

A recent multi-factorial study [73] on mass stranded sperm whales (*Physeter macrocephalus*) revealed relatively high levels of environmental pollutants, including organic Hg (MeHg), Se, Cd, with a Hg:Se ratio of 1:1. Also, opportunistic bacteria cultured from selected organs included representatives of *Vibrio*, *Aeromonas hydrophila* and *Enterococcus*. The authors concluded that these whales were presumably starved causing the mobilization of lipophilic contaminants which accumulated in the adipose tissue. These chemical compounds entered the blood circulation causing immuno- and neurotoxic effects which led to impaired

It is a generally accepted fact that that persistent organic pollutants (POPs) cause harm to human and animal tissue, earning them a reputation of 'the most widespread and toxic group of pollutants', as well as 'poisons without passports' [74-78]. Humans and animals worldwide were found to be carriers of POPs; from trace up to harmful amounts in their bodies [79-81]. Persistent organic pollutants include the chlorinated pesticides aldrin, dieldrin, dichlorodiphenyltrichloroethane (DDT), endrin, heptachlor, hexachlorobenzene, mirex and toxaphene, as well as industrial chemicals like PCBs, and the unwanted waste byproducts polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/F), and brominated flame retardants [75]. These chemicals have common, but distinct chemical and physical

POPs 'persist' in a certain environment resisting physical, chemical and/or biological

 POPs are transported via air/water currents over long distances because they are semivolatile causing them to evaporate slowly and enter the atmosphere. They then return to earth in rain and snow in colder areas leading to accumulation in regions such as the

Arctic which is thousands of kilometres away from their source;

 POPs have a low water and high lipid solubility, resulting in bio-accumulation in the fatty tissue of living organisms and cannot be excreted readily. Also, bio-magnification occurs causing an accumulation effect by factors of many thousands or even millions, as these compounds move up food chains [74, 77, 80, 82].

These chemical compounds are primarily products and by-products of industrial processes, synthetic chemical manufacturing and waste incineration ([80, 81]. Their existence dates back to the industrial boom after World War II, but are currently ubiquitous, and are found in food as well as soil, the atmosphere and various water bodies. In 2001, the United Nations Environment Program (UNEP) completed global negotiations with the signing of the socalled Stockholm convention on banning certain POPs, collectively known as the 'dirty dozen'. During this assessment, certain criteria for the identification and listing of chemicals under the convention were identified. New POPs that were identified during the survey include butylated tin, methylated mercury and polyaromatic hydrocarbon (PAH), as well as other less studied compounds such as chlorinated paraffin's, brominated diphenyl ethers and other flame retardants.

The big concern caused by organo-chlorines is because of growing evidence that these compounds act as endocrine disruptors [79, 83]. The U.S. EPA [83] report defined endocrine disruptors as 'exogenous agents that interfere with the synthesis, secretion, transport, binding, action or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis, reproduction, development and/or behaviour'. The science of endocrine disruption is still very new (only about 2 decades) and long term studies with effect results are therefore still preliminary [80]. The hormone disrupting effects differ according to the exposure situation and depend on the relative occurrence of the active congeners, specifically on the trophic level from which the food originates. For example, contaminants in the marine food chain of the Arctic Inuit population follow a very long passage. The result is that the higher, slowly metabolized, higher chlorinated PCBs will dominate over the lower chlorinated and more readily metabolized congeners. This situation will therefore create a specific effect on the hormonal balance, which will be different from other populations exposed more directly to the sources of these contaminants [76]. Toxic contaminants can also act as causal or aggravating factors in the development of a range of metabolic disorders. Several studies reported a correlation between metabolic disorders such as diabetes and cardiovascular disease, and lipid adjusted serum levels of substances like PCBs and dioxins. At present, 80% of the adult Greenlandic human population has PCB serum values in excess of 10 µg/l; a concentration shown to cause increased incidences of diabetes. Processes related to the development of metabolic disorders in which toxic contaminants may play an aggravating role include: (1) Proinflammatory effect through the formation of pro-inflammatory cytokines, oxidative stress and/or the formation of reactive oxygen species, (2) modulation of fatty acid metabolism, (3) influence on nuclear receptors, (4) effects on steroidogenesis, and (5) influence on uric acid levels [76].

In cetaceans, POP pollution has been documented to cause a variety of species-specific and congener-specific toxic and physiological effects. These include the formation of cancers, reproductive and endocrine impairment, skeletal anomalies, immune-suppression, as well as organ-specific disorders [1, 79, 84]. Also, the POP effects are often not seen in the exposed generation but rather in the second or third generation offspring [83, 85]. Since these compounds are lipophilic, they accumulate in the blubber of cetaceans and other marine mammals [84]. In cetaceans, PCBs are a recognized immuno-suppressant and many researchers believe that high levels of these and other POPs reduce resistance of these animals to disease due to their poor ability to metabolize these compounds [1, 58, 79, 84]. If contamination levels are high enough, it is possible for marine pollution to cause outright deaths of cetaceans. One such case was in the St. Lawrence Estuary in Canada where a marine reserve was established for a resident population of beluga whales. At the time of the article, about one beluga corpse was being washed up every week. These whales had signs of depressed immune systems, complications with digestive systems and carcinogenic tumours. Clinical testing revealed levels of contamination so high that the corpses had to be treated as toxic waste under the Canadian legislation [86].

Cutaneous Lesions in Cetaceans: An Indicator of Ecosystem Status? 143

Under natural conditions and in a pristine environment, cetacean skin usually acts as an effective barrier against the environment, as well as against potential pathogenic microbes. The relatively thick, keratin-rich skin provides a physical barrier against injury and penetration by pathogens, while immune cells of both the innate and adaptive immune system occur in the skin. Despite this seemingly formidable barrier numerous different skin lesions were reported on cetaceans all over the globe during past decades. Many microbial species, including known pathogens, were found to be associated with the lesions. Viruses, bacteria and fungi were frequently encountered in the lesions, which seems to be more prevalent among immuno-compromised cetacean populations, and those subjected to

Typical toxic pollutants that enter the coastal waters via urban effluents all over the globe are heavy metals, POPs and plastics. The detrimental effects of these toxins on mammalian physiology are well known and include neuro-toxic effects, endocrine disruption, harmful effects on the reproductive system, as well as an impaired immune system. The latter would render mammals, including cetaceans, more susceptible to microbial infections. Moreover, taking into account that the large volumes of sewage effluents entering the oceans contain opportunistic pathogens, such as keratinophilic fungi, the development of skin lesions on a cetacean with an already compromised immune system as a result of toxic pollutants, seems

Numerous case studies were reported where skin lesions were found on cetaceans from polluted waters. However, a clear connection between pollution levels and lesion incidence based on sound statistical analyses was not established. Nevertheless, surveys conducted on similar dolphin populations subjected to different levels of pollution, indicated that skin lesions among these animals were more prevalent in populations subjected to a polluted environment. Considering these results, together with known physiological effects of toxic pollutants, skin lesions among cetaceans may be indicative of an ecosystem under severe pressure as a result of anthropogenic activities. Since pollution levels are increasing in all the oceans of the world, it is imperative that more correlations between cetacean skin lesions and pollution levels be expediently studied on ecosystem, organismal, cellular and subcellular levels. The findings of such studies can be used by decision makers to manage anthropogenic activities, in such a manner that pollution to the marine environment is

**7. Conclusions** 

pollution.

inevitable.

reduced for a sustainable planet.

and Alfred Botha

*Department of Microbiology, University of Stellenbosch, Stellenbosch, South Africa* 

**Author details** 

Corresponding Author

Marnel Mouton\*

 \*

### **6.4. Plastics**

Plastics are widely used globally for packaging and storage, because they are relatively inexpensive, light weight, convenient and do not break easily. However, they also create widespread environmental concerns, because they are manufactured from petroleum, which is a non-renewable and usually imported resource [87]. Moreover, plastics degrade very slowly, resulting in alarming volumes ending up in landfills and the marine environment. Plastics also present a health hazard. Cooking and storing food in plastic containers cause migration of chemicals, such as Bisphenol A (BPA), into food and beverages. Types of plastics that have been shown to leach these substances are polycarbonate, polyvinyl chloride (PVC) and styrene. Interestingly, the leaching effect increases with heating, freezing and contact with oily or fatty food. A number of studies revealed evidence that human and wildlife populations are exposed to levels of BPA high enough to cause harmful developmental and reproductive effects in a number of species and laboratory animal studies [88]. Canada's government ruled in April 2008 that BPA is harmful to infants and toddlers and announced plans to ban certain products. Some states in the USA are also considering bills to restrict or ban BPA from children's products (Reuters, 14 September 2008). However, after considering extensive research, the European Commission concluded (2008) that products containing BPA were safe for consumers, as long as the products were used as indicated by the manufacturer. In Canada, a ban on the importation, sale and advertising of polycarbonate baby bottles was enforced, together with implementation of efforts to reduce levels of BPA in infant formula, to the lowest achievable concentrations. The use of water bottles, sport bottles, sport equipment, etc. was considered to be safe and exposure from these, regarded to be very low. However, BPA was listed as 'CEPA toxic' in Canada in October 2010, to allow Environment Canada to establish water quality standard to restrict BPA levels in effluent discharges to the environment [89]. BPA is a common component of wastewater entering the oceans [90-92].
